ABSTRACT Approximately 60.3% of those aged 20 to 39 years are overweight or obese, and excess weight gain in young adulthood is associated with future weight gain, cardiovascular disease risk factors, and psychological distress. Consequently, it has been suggested that treating overweight and obesity in young adults may prevent chronic disease in middle age. Relatively little is known about how to promote weight loss in this population without using costly in-person programs that have limited scalability. For several years, our group has investigated the efficacy of interventions that rely on ubiquitous technologies to meet young adults in the virtual spaces they frequently inhabit and use these venues to promote weight loss through physical activity and healthy diet. We now propose to conduct a parallel-group randomized controlled trial among 642 overweight/obese university students aged 18-35 years in San Diego. Participants will be randomly allocated to either 1) SMART 2.0 with technology and personal health coaching; 2) SMART 2.0 with technology alone; or 3) a control group. The interventions will be delivered for 24 months, and they are designed to maximize efficacy in a scalable manner. Intervention content will be delivered using a fully integrated system of modalities: 1) Fitbit, 2) MyFitnessPal, 3) SMS, 4) multiple social media streams, 5) a website with blog, and 6) email. Consumer-level devices and apps will be used to self-monitor behavior, and their data will be passively acquired in real-time. Algorithms will be used to automatically deliver interactive text messages to support individually tailored goal setting, performance feedback, and goal review in a highly dynamic style that reflects participants' behavioral progress towards achieving a minimum goal of 5% weight loss. Participants will be encouraged to share their data and behavioral progress with others via social networking tools built into the apps. Social network mechanisms of influence will be used both within the study-space, to elicit participant-to-participant and health coach-to- participant support, as well as outside the study-space, to invoke social support and accountability from strong ties known to be important for long-term behavior change. Additionally, one group will receive monthly technology-mediated, real-time personal health coaching that is theory- and evidence-based. Our primary aim is to determine the efficacy of the SMART 2.0 interventions to improve weight over 24 months. Our secondary aims are to evaluate to evaluate 1) differences between groups at 6, 12, 18, and 24 months in anthropometric and physiological outcomes, physical activity, diet, sleep, self-esteem, body image, anxiety, depression, and the frequency and composition of participants' online communication about weight-related behaviors; 2) the dose response (i.e., quantified engagement with modalities) of the interventions; 3) the usability and acceptability of the intervention; 4) potential mediators and moderators of the intervention effects (e.g., social network connectivity, contamination, etc.); and 5) patterns of change in physical activity, diet, and sleep.